1. Field of the Invention
The present invention relates to a method of determining a reflective surface of a reflector in a vehicle lamp used in vehicles such as automobiles and the like.
2. Related Background Art
The vehicle lamps need to meet (1) the conditions from the aspect concerning the function as lamps and, in addition thereto, (2) the conditions from the aspect concerning the shape (shape constraints) and (3) the conditions from the aspect concerning the appearance (appearance constraints) because of their use in a mounted state on the vehicles such as the automobiles and the like. It is thus necessary to realize lamps optimized as to the conditions from the functional aspect while satisfying the given constraints from the shape aspect and the appearance aspect.
The conditions from the functional aspect include light uniformity with which the entire lamp lights uniformly, light diffusibility with which light is properly diffused to be observed from various directions, and so on, depending upon types of lamps.
As for the constraints from the vehicle and body side, the shape constraints include conditions defined by the volume and shape of lamp receiving portions of the body, the continuous shape of the outer surface of the lamp (the outer surface of lens) from the other body portions, and so on. The appearance constraints include conditions resulting from harmony with the appearance of the other body portions, requirements from the design aspect of the body, and so on.
In recent years, there are increasing needs for lamps meeting strict shape constraints, e.g., further decrease in the depth of the lamp, because of restrictions on the lamp receiving portions from the aspect of construction of the body, the increasing tendency toward fascinating styling of cars, and so on. Under such circumstances, when a lamp was constructed, for example, using a reflector wherein the basic shape of its reflective surface was a unifocal paraboloid, decrease was insufficient in the thickness of the lamp and it was difficult to comply with the above-stated shape constraints such as the decrease in the depth of the lamp.
As against it, another reflector was proposed in such structure that the basic shape of the reflective surface was a free-formed surface created so as to match the shape constraints and other conditions. With use of the free-formed surface, it is relatively easy to meet the shape constraints such as the decrease in the depth of the lamp because of its degrees of freedom in designing thereof (for example, reference is made to Japanese Patent Application Laid-Open No. H09-33708). However, since reflective surface shapes of respective portions in the reflective surface need to satisfy the conditions from the functional aspect of reflecting the light from the light source into the direction along the given optical axis, they are normally formed in the shape of paraboloid of revolution or in the shape approximate thereto with light diffusing capability. Therefore, it is common practice to form the reflective surface by dividing the above-stated free-formed surface into a plurality of segments and assigning reflective surface elements having respective, reflective surface shapes of paraboloids of revolution to the respective segments.
In creating the reflective surface with the basic shape of the free-formed surface as described above, however, the shape often largely differs depending upon individual lamps, and the free-formed surface is often asymmetric because of the given shape constraints and the like. Therefore, there was the problem of complicated design steps for creating the segments on the free-formed surface used for determination of the reflective surface in each reflector and for determining the reflective surface shapes of the reflective surface elements assigned to the respective segments.
The present invention has been accomplished in view of the above problems and an object of the present invention is thus to provide a method of determining a reflective surface of a reflector in a vehicle lamp, which permits efficient creation of the segments on the free-formed surface and efficient creation of the reflective surface elements assigned to the respective segments.
In order to accomplish the above object, a method of determining a reflective surface of a reflector used in a vehicle lamp according to the present invention is a method comprising: (1) a free-formed surface creating step of creating a free-formed surface satisfying a predetermined shape constraint; (2) a reference plane defining step of defining a reference plane as a plane facing the free-formed surface; (3) a reference segment creating step of creating a reflective surface outline on the reference plane and dividing a region on the reference plane including the interior of the reflective surface outline, into a plurality of reference segments; (4) a representative point creating step of selecting reference representative points for the respective reference segments and projecting the reference segments and the reference representative points onto the free-formed surface, thereby creating dividing segments of the free-formed surface and representative points specifying positions for determining surface shapes in the segments; (5) a surface shape determining step of finding shape parameters at the representative points for the respective segments and determining the surface shapes in the segments, based on the shape parameters; and (6) a reflective surface determining step of assigning reflective surface elements having the surface shapes determined, to the respective segments to determine a reflective surface comprising a plurality of the reflective surface elements.
In the above reflective surface determining method, for the free-formed surface created as the basic shape of the reflective surface so as to satisfy the shape constraint from the body side, the steps of dividing it into segments and determining the surface shapes of the reflective surface elements assigned to the respective segments are not carried out directly on the free-formed surface the shape of which is complex and varies depending upon the reflective surface to be designed, but are done on the opposite reference plane defined separately. When the steps for determination of the reflective surface are not executed on the free-formed surface, but on the reference plane in this way, uniform handling becomes feasible independent of the shape of the reflective surface to be designed, which simplifies the design steps of the reflective surface.
The reference plane defined as a plane facing the free-formed surface is a plane equivalent to the field where an observer observes the reflector or the lamp. Therefore, when the reflective surface is created by making use of this reference plane, it becomes feasible to gain the reflective surface formed in the suitable shape and appearance of the reflective surface when observed from its axial direction, and provided with preferable light reflection characteristics.
Further, the determination of surface shape can be made more efficient when the surface shape is determined by selecting a representative point for each of the segments obtained by division. Particularly, when the representative points are also determined based on the selection of reference representative points in the reference segments on the reference plane, it becomes feasible to select the representative points on a uniform basis, independent of the shape of the free-formed surface.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.